Linkage system

ABSTRACT

A linkage system which offers high rigidity and good assemblability and producibility, and enables parts such as rotary transmission components and actuators to be readily installed. A linkage system includes an input member disposed on an input side, an output member disposed on an output side, and three or more link mechanisms, each link mechanism consisting of end links rotatably coupled to the input member and the output member, respectively, a center link rotatably coupled to the end links on the input side and the output side, and four revolute joints by which the end links are rotatably coupled to the input and output members, and to the center link. The link mechanism being geometrically identical with respect to a center cross-sectional plane relative on the input and output sides. Each of the revolute joints of the link mechanism includes bearings that support at both ends of the revolute joint.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a linkage system used, for example, fora joint of an articulated robot that performs complex processing orhandling of goods in a three-dimensional space at high speed and withhigh precision.

2. Description of the Related Art

For example, Japanese Patent Laid-Open Publication No. 2000-94245discloses a linkage system with a parallel link mechanism that performscomplex processing or handling of goods in a three-dimensional space athigh speed and with high precision.

The parallel link mechanism adopted in such a linkage system includes aplurality of links that connect a base plate and a traveling plate andcooperatively extend and retract to change the position and orientationof the traveling plate relative to the base plate. Tool is attached tothe traveling plate of the parallel link mechanism, while a workpiece isheld on a table which is designed rotatable so that the tool can freelychange its position and orientation relative to the workpiece on thetable and perform complex processing or handling of goods by the tool ona three-dimensional basis.

Characteristic features of such a parallel link mechanism are that theweight of the movable parts can be reduced, and positioning errors ofseveral links are evened-out at the distal ends, both of which areadvantageous for the complex, high-speed, and high-precision processingor handling of goods in the three-dimensional space.

On the other hand, if the operating range of the traveling plate needsto be increased in the parallel link mechanism, the links have to beextended because each link has a relatively small operating angle range,and the entire mechanism and then the system itself become bulky.Further, because of relatively low rigidity of the entire mechanism, theweight of the tool, or the load capacity of the traveling plate, has tobe limited to a small range.

To solve the problems, the applicant of the present invention has fileda patent application relating to a linkage system with compact linkmechanisms having high rigidity and large load capacity (Japanese PatentApplication No. 2003-40086).

The linkage system includes three or more link mechanisms. Each linkmechanism consists of end links rotatably coupled to link hubs of inputand output members, respectively, and a center link to which the endlinks are rotatably coupled, and is geometrically identical with respectto the center cross-sectional plane on the input and output sides. Eachlink mechanism forms a three-link chain with four revolute joints.

In this linkage system, bearing structure is built in the link hubs,wherein outer rings of the bearing are embedded in the link hubs whileinner rings of the bearing are coupled to the end links. Rotarytransmission components are disposed in the space left in the linkmechanisms, where drive mechanisms such as actuators are also placed forposition control of the end links through the rotary transmissioncomponents, so that the output-side link hub is moved with two degreesof freedom, by driving the rotary transmission components, relative tothe stationary input-side link hub.

While the linkage system is obviously operated by controlling therotation angles of the end links, the previous patent application didnot show any specific control method, nor the methods of how todetermine the orientation of the output-side link hub from inputrotation angles of the input-side link hub, or how to determine therotation angles of the input-side link hubs from input data regardingthe orientation of the output-side link hub.

Consequently, the present applicant has filed another patent application(Japanese Patent Application No. 2003-287945) based on the previousapplication (Japanese Patent Application No. 2003-40086), relating to alinkage system in which the methods of determining the orientation ofthe output-side link hub from input rotation angles of the input-sidelink hub or the rotation angles of the input-side link hubs from inputdata regarding the orientation of the output-side link hub.

However, there is still scope of improvement in the link mechanismsshown in these patent applications. For example, the rigidity of thelink mechanism is not satisfactorily high because of cantileveredstructure at the revolute joints thereof. The assemblability of the linkmechanism is poor because the input-side and output-side link hubs, endlinks, and center links are coupled to each other with revolute joints.Furthermore, because these parts each have a complex shape, they do notlend themselves to be readily produced.

In the linkage system, the rotary transmission components are disposedin the space left in the link mechanism and the actuators for positioncontrol of the end links are provided through the rotary transmissioncomponents. Another problem was that there was little freedom ofinstallation of the rotary transmission components and actuators becausethe space left in the link mechanism was small. It was hard to installother necessary parts that were large, such as rotation angle sensingmeans for measuring rotational angles of the input-side end links.

SUMMARY OF THE INVENTION

Based on the foregoing, an object of the present invention is to providea linkage system that offers high rigidity and good assemblability andproducibility, and enables parts such as rotary transmission componentsand actuators to be readily installed.

To achieve the object, the invention provides a linkage system includingan input member disposed on an input side, an output member disposed onan output side, and three or more link mechanisms, each link mechanismconsisting of end links rotatably coupled to the input member and theoutput member, respectively, a center link rotatably coupled to the endlinks on the input side and the output side, and four revolute joints bywhich the end links are rotatably coupled to the input and outputmembers, and to the center link, the link mechanism being geometricallyidentical with respect to a center cross-sectional plane relative on theinput and output sides, wherein each of the revolute joints of the linkmechanism includes bearings that support at both ends of the revolutejoint.

The bearings that support at both ends of each revolute joint of thelink mechanism improve the rigidity at the bearings and of the linkmechanism itself. The bearing structure enables the link mechanismcomponents to be detachable at parts other than the revolute joints andimproves assemblability and producibility of the link mechanisms, whichin turn enables size reduction of the link mechanisms.

The revolute joints of the link mechanism may preferably be detachablefrom the links. This makes it possible to disassemble the bearings inthe revolute joints into separate units. Each component can then have asimple shape and be produced more easily, leading to improvedmass-producibility.

The three or more link mechanisms disposed between the input and outputsides are geometrically identical with each other so as to construct amechanism with two degrees of freedom. “Geometrically identical withrespect to the center cross-sectional plane on the input and outputsides” means that each link mechanism is geometrically identical on theinput and output sides if it is divided along the symmetrical plane ofthe center link.

Each link forms a three-link chain with four revolute joints. The endlinks on both input and output sides share the same center, each endlink being equally distanced from the center, forming a sphericallinkage. The centers of the spherical linkages of the three or more linkmechanisms are coincide with one another. The two coupling shafts of therevolute joints at both ends of the center links for connecting the endlinks can either be arranged at an angle or parallel with each other.Either way, all the center links have a geometrically identicalconstruction to one another.

It is desirable that rotation angle sensing means for measuring therotation angle of the end links be provided at the revolute jointsbetween the input member and preferably two or more end links. Therotation angle sensing means may include a sensor and a sensed partrespectively placed in a rotating part and a stationary part oppositeeach other so as to save installation space. Actuators are connected tothe end links on the input side through rotary transmission components.Using the following equation, orientation control of the output membercan be achieved by reverse conversion, or reversely, the orientation ofthe output member can be determined from the equation. The equationrepresents the correlation between the orientation of the output memberdefined by its bending angle θ and revolution angle φ and rotationangles βn of the end links on the input side:cos(θ/2)sin βn−sin(θ/2)sin(φ+δn)cos βn+sin(γ/2)=0where γ is an axial angle between the two coupling shafts at both endsof the center links, and δ is a distance angle of circumferentialdistance of each end link from a reference end link.

The “bending angle θ” of the orientation of the output member is theinclination angle of the output member from the vertical center axis ofthe input member, and the “revolution angle φ” thereof is the rotationangle in a horizontal plane of the inclined output member relative tothe center axis of the input member. The “rotation angle βn” thereof isthe turning angle of the end link at one end that is rotatably connectedto the input member. The “axial angle γ” thereof is the angle betweenthe coupling shaft of a revolute joint at one end of a center linkrotatably coupled to the end link on the input side and the couplingshaft of a revolute joint at the other end of the center link rotatablycoupled to the end link on the output side. The “distance angle δ”thereof is the angle between the shafts of the revolute joints ofcircumferentially arranged end links coupled to the input member, anddefines the circumferential distance of each end link from a referenceend link. “Reverse conversion using the equation” means inputting targetvalues that define the orientation of the output member in the equationto obtain necessary rotation angles of the end links on the input side.

Any one of the input member and the output member should preferablyinclude a rotating mechanism that makes the output member rotate aroundits center axis so as to enable the output member to move with threedegrees of freedom by adding a degree of rotation freedom to the twodegrees of freedom. It is desirable that this rotating mechanism alsoinclude rotation angle sensing means.

If the rotating mechanism is provided to the input member in themechanism with three degrees of freedom, the orientation of the outputmember in the link coordinate is defined by the bending angle θ_(L), therevolution angle φ_(L), and a surface rotation angle η_(L) of the outputmember. In this case, the correlation between the orientation of theoutput member and the rotation angles βn of the end links on the inputside is represented by the following equations:cos(θ_(L)/2)sin βn−sin(θ_(L)/2)sin(φ_(L) +δn)cos βn+sin(γ/2)=0where γ is the axial angle between the two coupling shafts at both endsof the center links, and δ is the distance angle of circumferentialdistance of each end link from a reference end link; and

-   η_(L)=φ_(L). Orientation control of the output member is achieved by    reverse conversion using the equation, or reversely, the orientation    (three degrees of freedom) of the output member is determined from    the equation.

In a global coordinate system, the orientation of the output member (thebending angle θ_(G), the revolution angle φ_(G), and the surfacerotation angle η_(G)) is θ_(G)=θ_(L), φ_(G)=φ_(L)+m, η_(G)=η_(L), wherem is the rotation angle of the input member.

If the rotating mechanism is provided to the output member in themechanism with three degrees of freedom, the orientation of the outputmember in the link coordinate is defined by the bending angle θ_(L), therevolution angle φ_(L), and the surface rotation angle η_(L) of theoutput member. The correlation between the orientation of the outputmember, the rotation angles βn of the end links on the input side, andthe rotation angle m of the output member is represented by thefollowing equations:cos(θ_(L)/2)sin βn−sin(θ_(L)/2)sin(φ_(L) +δn)cos βn+sin(δ/2)=0where γ is the axial angle between the two coupling shafts at both endsof the center links, and δ is the distance angle of circumferentialdistance of each end link from a reference end link; and

-   η_(L)=m. Orientation control of the output member is achieved by    reverse conversion using the equation, or reversely, the orientation    (three degrees of freedom) of the output member is determined from    the equation.

In the foregoing configurations, a linear drive mechanism can beprovided to any one of the input member, the output member, and thecenter links, to achieve end position control of the output memberwhereby a member attached to the output member can more readily becontacted with a predetermined point.

Furthermore, it is desirable that any one of the input and outputmembers include a torque sensor so as to detect torque input from theother one that is not provided with the sensor. For example, a torquesensor can be provided to the input member to detect torsion torque ofthe output member.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view of one embodiment of a rotation symmetrytype linkage system of the invention having three link mechanisms;

FIG. 2 is a perspective view of one embodiment of a mirror symmetry typelinkage system of the invention having three link mechanisms;

FIG. 3 is a cross-sectional view of revolute joints between the inputmember and end links on the input side of the linkage systems of FIGS. 1and 2;

FIG. 4 is a perspective view of one embodiment of a linkage systemprovided with actuators on the input side;

FIG. 5 is a perspective view of another embodiment of a linkage systemwith link mechanisms having non-right angled arms; and

FIG. 6 is a perspective view of still another embodiment of a linkagesystem with six link mechanisms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show linkage systems of the invention used, for example,for a joint of an articulated robot that performs complex processing orhandling of goods in a three-dimensional space at high speed and withhigh precision. The system includes three sets of link mechanisms 1 to3, which have a geometrically identical construction to one another. Thebasic structure of the link mechanisms 1 to 3 is as disclosed in theJapanese Patent Application No. 2003-40086 previously filed by thepresent applicant.

As shown in FIGS. 1 and 2, the link mechanism 1 (2, 3) forms athree-link chain, including an end link 1 a (2 a, 3 a) provided on theinput side and rotatably coupled to a disk-like input member 4, an endlink 1 c (2 c, 3 c) provided on the output side and rotatably coupled toa disk-like output member 5, a center link 1 b (2 b, 3 b) rotatablycoupled to both the end links 1 a (2 a, 3 a) and 1 c (2 c, 3 c) toconnect both the end links, and four revolute joints 6 a (7 a, 8 a), 6 b₁ (7 b ₁, 8 b ₁), 6 b ₂ (7 b ₂, 8 b ₂), and 6 c (7 c, 8 c).

The end links 1 a to 3 a and 1 c and 3 c of the three link mechanisms 1and 3 share the same center, each link being equally distanced from thecenter, forming a spherical linkage. The two coupling shafts of therevolute joints 6 b ₁ and 6 b ₂ (7 b ₁ and 7 b ₂, 8 b ₁ and 8 b ₂) atboth ends of the center link 1 b (2 b, 3 b) coupled to the end links 1 aand 1 c (2 a and 2 c, 3 a and 3 c) may be arranged at an angle, orarranged parallel with each other. Either way, all the center links 1 bto 3 b have a geometrically identical construction to one another.

FIG. 1 shows one embodiment wherein the link mechanisms 1 to 3 are of arotation symmetry type. The input member 4 and the end links 1 a to 3 aon the input side are positioned in rotation symmetry with the outputmember 5 and the end links 1 c to 3 c on the output side, relative tothe center lines of the center links 1 b to 3 b. The drawing shows astate wherein the output member 5 is angled to the input member 4 with acertain operational angle.

FIG. 2 shows one embodiment wherein the link mechanisms 1 to 3 are of amirror symmetry type. The input member 4 and the end links 1 a to 3 a onthe input side are positioned in mirror symmetry with the output member5 and the end links 1 c to 3 c on the output side, relative to thecenter lines of the center links 1 b to 3 b. The drawing shows a statewherein the output member 5 is angled to the input member 4 with acertain operational angle.

FIG. 3 shows the revolute joints 6 a to 8 a between the end links 1 a to3 a on the input side and the input member 4 of the above twoembodiments. On the top face of the disk-like input member 4 aredisposed three pairs of support members 11 a to 13 a for the respectivelink mechanisms 1 to 3. Each pair of the support members 11 a (12 a, 13a) is provided with bearings 17 a (18 a, 19 a) that rotatably support ashaft 14 a (15 a, 16 a). One arm end of each end link 1 a (2 a, 3 a),which is L-shaped, is coupled to the shaft 14 a (15 a, 16 a) between thepair of support members 11 a (12 a, 13 a). The support members 11 a to13 a are detachably attached to the input member 4 using screws or thelike, but they can be formed integrally with the input member 4.

The arm end of the end link 1 a (2 a, 3 a) is fixed to the shaft 14 a(15 a, 16 a) using setscrews. One end of the shaft 14 a (15 a, 16 a) isfastened to the bearings 17 a (18 a, 19 a) with some preload bytightening with a nut 20 a (21 a, 22 a) and a washer.

The support members 11 a to 13 a need not be equally located incircumferential direction, but the circumferential positions of thesupport members on the input member 4 must be matched with those of thesupport members on the output member 5. The input member 4 and theoutput member 5 are shared by the three link mechanisms 1 to 3, the endlinks 1 a to 3 a and 1 c to 3 c being coupled to their respectivesupport members 11 a to 13 a and 11 c to 13 c. While the input member 4and output member 5 are illustrated as disks, they can be of any shapeas long as they have enough space for the support members 11 a to 13 a,and 11 c to 13 c. They can be formed with through holes for the purposeof wiring.

The description of the output-side revolute joints 6 c to 8 c thatcouple the output member 5 with the end links 1 c to 3 c on the outputside will be omitted as they have the same structure as that of theinput-side revolute joints 6 a to 8 a.

The other arm end of the end link 1 a (2 a, 3 a) on the input side iscoupled to one end of the substantially L-shaped center link 1 b (2 b, 3b) at the revolute joint 6 b ₁ (7 b ₁, 8 b ₁). A pair of support members11 b ₁ (12 b ₁, 13 b ₁) is provided to the one end of the center link 1b (2 b, 3 b). Bearings (not shown) are attached to the pair of supportmembers 11 b ₁ (12 b ₁, 13 b ₁) and rotatably support a shaft 14 b ₁ (15b ₁, 16 b ₁). The other arm end of the L-shaped end link 1 a (2 a, 3 a)is coupled to the shaft 14 b ₁ (15 b ₁, 16 b ₁) between the pair ofsupport members 11 b ₁ (12 b ₁, 13 b ₁). The support members 11 b ₁ (12b ₁, 13 b ₁) are detachably attached to the center link 1 b (2 b, 3 b)using screws or the like, but they can be formed integrally with thecenter link.

The arm ends of the end links 1 a to 3 a are fixed to the shafts 14 b ₁,to 16 b ₁ using setscrews. Instead, they can be fixed using keys orD-cut shafts. One end of the shafts 14 b ₁ to 16 b ₁ is fastened to thebearings with some preload by tightening with nuts and washers.

The description of the revolute joints 6 b ₂ to 8 b ₂ that couple theother arm ends of the end links 1 c to 3 c on the output side with theother ends of the center links 1 b to 3 b will be omitted as they havethe same structure as that of the revolute joints 6 b ₁ to 8 b ₁.

In the link mechanisms 1 to 3, when the angle and length of the shafts14 a to 16 a and the geometrical construction of the input end links 1 ato 3 a on the input side are identical with those on the output side,and the center links 1 b to 3 b have the same shape on both the inputand output sides, and when the end links 1 a to 3 a on the input sideare coupled to the input member 4 and to the center links 1 b and 3 b atthe same angular positions as those on the output side relative to thesymmetrical plane of the center links 1 b to 3 b, then the input member4 and the end links 1 a to 3 a on the input side move identically withthe output member 5 and the end links 1 c to 3 c on the output side dueto its geometrical symmetry, rotating at the same speed with the samerotation angle on both the input and output sides. The symmetrical planeof the center links 1 b to 3 b is here called “constant velocitybisecting plane.”

As the center links 1 b to 3 b move along the constant velocitybisecting plane, the circumferentially arranged, geometrically identicallink mechanisms 1 to 3 between the input member 4 and output member 5can move without interfering with each other, the end links rotating atthe same speed on both the input and output sides at any angle.

Because of the bearing structure of the four revolute joints 6 a to 8 a,6 b ₁ to 8 b ₁, 6 b ₂ to 8 b ₂, and 6 c to 8 c, namely, the couplingportions between the input member 4 and the end links 1 a to 3 a,between the input-side end links 1 a to 3 a and the center links 1 b to3 b, between the center links 1 b to 3 b and the output-side end links 1c to 3 c, and between the output-side end links 1 c to 3 c and theoutput member 5, of the respective link mechanisms 1 to 3, frictionresistance or rotation resistance at the coupling portions is reduced,whereby smooth power transmission is secured and durability improved.The bearing structure offers improved rigidity as it provides support atboth ends in the revolute joints 6 a to 8 a, 6 b ₁ to 8 b ₁, 6 b ₂ to 8b ₂, and 6 c to 8 c. Furthermore, the structure enables the linkcomponents to be detachable at parts other than the revolute joints,offering better assemblability.

FIGS. 4 and 5 show linkage systems wherein actuators 31 and 32 areprovided to two of the input end links 1 a and 3 a (2 a and 3 a in FIG.5). The link mechanisms 1 to 3 are of a mirror symmetry type. The inputmember 4 and the output member 5 are larger and the revolute joints 6 ato 8 a, and 6 c to 8 c are wider in this embodiment. The rotation axesof the revolute joints 6 b ₂ to 8 b ₂ that couple the end links 1 c to 3c and the center links 1 b to 3 b are all oriented toward the centeraxis of the input member 4. Therefore, while the angle between theshafts at both arm ends of each end link is not 90°, the input side andthe output side of each end link are geometrically identical. (In thecase where this angle is not 90°, the equation to be described later isnot valid relating to the end links 1 a to 3 a and the orientation ofthe output member 5.) Thus the end links 1 a to 3 a, and 1 c to 3 c andthe center links 1 b to 3 b can move without interfering with eachother. In these embodiments, also, the link mechanisms 1 to 3 form alarger space S inside, enabling easy installation of various parts suchas actuators and rotation angle sensing means, and offering highstability because of enlarged center of gravity (see FIG. 5). FIG. 6shows a linkage system having six link mechanisms 1 to 3, and 1′ to 3′to enlarge the area of center of gravity and to increase rigidity.

In the embodiments shown in FIGS. 4 and 5, the shafts 14 a to 16 acoupled to the arm ends of the end links 1 a to 3 a on the input sideare coaxially connected to the output shafts of actuators such asmotors. A movable part, for example, a robot arm (not shown) mounted onthe output member 5 is manipulated by controlling the rotation angles ofthe end links 1 a to 3 a using these actuators.

Alternatively, the actuators for rotation angle control can be connectedto the revolute joints 6 a to 8 a between the input member 4 and the endlinks 1 a to 3 a on the input side via rotary transmission components(not shown). For example, an actuator such as a motor can be connectedto a gear attached to one end of the shaft 14 a (15 a, 16 a) supportedby the support members 11 a (12 a, 13 a) with the bearings 17 a (18 a,19 a). The actuator that is accommodated in a housing (not shown) can beplaced below the input member 4 and connected to the gear through a holeformed in the input member 4.

In another embodiment, rotation angle sensors (not shown) are providedto the shafts 14 a to 16 a supporting the input-side end links 1 a to 3a, respectively. Using such sensors makes the actuators more compact asthey do not then need a servo mechanism, and makes it unnecessary todetermine the position of the origin each time power is turned on.

The shafts 14 a to 16 a are supported by inner (rotating) rings of thebearings 17 a to 19 a, and the outer (non-rotating) rings of thebearings 17 a to 19 a are fixed to the support members 11 a to 13 a ofthe input member 4. The rotation angle sensor consists of a sensed partprovided to the inner end of the shaft 14 a (15 a, 16 a) and a sensormounted on the input member 4 opposite the sensed part. While the sensedpart is disposed on the rotating side and the sensor on the stationaryside in this embodiment, the sensor can be mounted on the rotating sideand the sensed part on the stationary side because the sensed partrotates only within the range of about ±45°.

The sensed part is a radial type and consists, for example, of anannular back metal and a magnetic member at the outer periphery of theback metal having alternating N and S poles, the back metal beingfixedly attached to the shaft 14 a (15 a, 16 a). The magnetic member is,for example, a rubber magnet, which can be bonded to the back metal bycuring adhesion. The sensed part can also be a plastic magnet or asintered magnet, in which case the back metal is not absolutelynecessary.

The sensor consists of a magnetic sensor that is activated by a unipolaror alternating magnetic field and generates a square wave output signalcorresponding to magnetic flux density. The magnetic sensor is mountedon a magnetic sensor circuit board (not shown), which is encapsulated ina resin case and resin-molded. The resin case that accommodates themagnetic sensor and the circuit board is fixedly attached to the inputmember 4. The circuit board includes circuitry for controlling powersupply to the magnetic sensor and for processing output signals from thesensor for signal output. Wiring can be provided in the inner spacesurrounded by the link mechanisms.

When the sensed part rotates with the rotation of the shaft 14 a (15 a,16 a), the sensor generates output signals corresponding to the densityof magnetic flux generated by the magnetic member, so that the rotationangle of the shaft 14 a (15 a, 16 a), i.e., of the end link 1 a (2 a, 3a) is determined. While the magnetic sensor of this embodiment functionsas an encoder that generates A-phase or Z-phase output signal, thesensor can include another magnetic sensor so that it functions as theencoder generating A/B-phase or A/B/Z-phase output signal. Other meansor methods, for example, the means of sensing an absolute rotation angleshown in Japanese Patent Laid-Open Publication No. 2003-148999, or acoil sensor such as an optical fiber sensor or a resolver sensor, can beemployed for the sensed part and the sensor for use in the presentinvention.

Referring back to FIG. 1, the orientation of the output member 5 isdefined by its bending angle θ and revolution angle φ. Here, thecorrelation between the orientation of the output member 5 and therotation angles βn of the input-side end links 1 a to 3 a is expressedas follows:cos(θ/2)sin βn−sin(θ/2)sin(φ+δn)cos βn+sin(γ/2)=0where γ is an axial angle between the two coupling shafts at both endsof the center links, and δ is a distance angle of circumferentialdistance of each end link from a reference end link. Using thisequation, orientation control of the output member 5 is achieved byreverse conversion.

In other words, the orientation of the output member 5 can be defined bytwo degrees of freedom (bending angle θ and revolution angle φ).

More specifically, when the linkage system includes three linkmechanisms 1 to 3 and the end links 1 a to 3 a and 1 c to 3 c arecircumferentially equally distanced from each other as in thisembodiment, the correlation between the orientation of the output member5 (bending angle θ and revolution angle φ) and the rotation angles βn ofthe end links on the input side is defined by the following equations(where θ is the angle from vertical of the output member 5 relative tothe input member 4, φ is the rotation angle from 0° in horizontal planeof the output member 5 relative to the input member 4, β₁ and β₂ are therotation angles of two of the three input-side end links 1 a to 3 a atthe revolute joints 6 a to 8 a, γ is the angle between the shafts of therevolute joints 6 b ₁ to 8 b ₁ and 6 b ₂ to 8 b ₂ at both ends of thecenter links 1 b-3 b respectively coupled with the input-side andoutput-side end links 1 a to 3 a and 1 c to 3 c:cos (θ/2)sin   β₁ − sin (θ/2)sin   ϕcos  β₁ + sin (γ/2) = 0cos (θ/2)sin   β₂ − sin (θ/2)sin (ϕ + 120^(∘))cos   β₂ + sin (γ/2) = 0cos (θ/2)sin   β₃ − sin (θ/2)sin (ϕ + 120^(∘))cos   β₃ + sin (γ/2) = 0.

Orientation control of the output member 5 is achieved by reverseconversion using the equations, namely, by inputting target values θ andφ for defining a predetermined orientation and solving two or more ofthe above equations so as to obtain necessary rotation angles of theinput-side end links 1 a to 3 a corresponding to the input orientation.

Reversely, the orientation of the output member 5 is determined from theequations, namely, by inputting measured rotation angles of theinput-side end links 1 a to 3 a in the equations.

In case of adopting a stationary input member 4, revolutions of theoutput member 5 at a large bending angle relative to the stationaryinput member 4 requires a large torque. When the output member 5revolves at a constant bending angle from the vertical, the surface ofthe output member 5 also rotates, resulting in change in the directionof components mounted on the output member 5. In order to solve theabove-mentioned problem, by providing an additional actuator (not shown)to the input member 4 for the purpose of rotating the input member 4 inaddition to the two degrees of freedom of the link mechanisms 1 to 3,the output member 5 can be operated with three degrees of freedom. Insuch a mechanism with three degrees of freedom, the surface angle of theoutput member 5 can then be changed without changing the orientation ofthe link mechanisms 1 to 3.

The orientation of the output member 5 in a link coordinate of thismechanism with three degrees of freedom is defined by its bending angleθ_(L), revolution angle φ_(L), and surface rotation angle η_(L). Thefollowing equations represent the correlation between the orientation ofthe output member 5 and the rotation angles βn of the input-side endlinks 1 a to 3 a:cos(θ_(L)/2)sin βn−sin(θ_(L)/2)sin(φ_(L) +δn)cos βn+sin(γ/2)=0where γ is an axial angle between the two coupling shafts at both endsof the center links, and δ is a distance angle of circumferentialdistance of each end link from a reference end link; and

-   η_(L)=φ_(L). Orientation control of the output member 5 in the link    coordinate is achieved by reverse conversion using these equations.

In a global coordinate system, the orientation of the output member 5(the bending angle θ_(G), the revolution angle φ_(G), and the surfacerotation angle η_(G)) is θ_(G)=θ_(L), φ_(G)=φ_(L)+m, η_(G)=η_(L), wherem is the rotation angle of the input member.

Reversely, the orientation of the output member 5 in the mechanism withthree degrees of freedom is determined from the equations by inputtingmeasured rotation angles of the input-side end links 1 a to 3 a in theequations.

Alternatively, the actuator mentioned above can be provided to theoutput member 5. In this case, the orientation of the output member inthe link coordinate is defined by the bending angle θ_(L), therevolution angle φ_(L), and the surface rotation angle η_(L) of theoutput member 5. The correlation between the orientation of the outputmember 5, the rotation angles βn of the end links on the input side, andthe rotation angle m of the output member 5 is represented by thefollowing equations:cos(θ_(L)/2)sin βn−sin(θ_(L)/2)sin(φ_(L) +δn)cos βn+sin(γ/2)=0where γ is the axial angle between the two coupling shafts at both endsof the center links, and δ is the distance angle of circumferentialdistance of each end link from a reference end link; and

-   η_(L)=m. Likewise, orientation control of the output member 5 is    achieved by reverse conversion using these equations. Here, the link    coordinate is the same as the global coordinate.

Reversely, the orientation of the output member 5 in the mechanism withthree degrees of freedom is determined from these equations by inputtingmeasured rotation angles of the input-side end links 1 a to 3 a in theequations.

It is also possible to construct a mechanism with three degrees offreedom by providing a motor-driven linear actuator (not shown) to theoutput member 5. With a linear actuator, the end position control of theoutput member 5 is achieved, and the member attached to the outputmember 5 is more readily contacted with a target point. The linearactuator can be of a pneumatic or hydraulic type. Further, the linearactuator can be provided to, other than the output member 5, the inputmember 4, or placed between the pair of revolute joints of the centerlinks 1 b to 3 b, in which case the actuators are all driven a samedistance at the same time.

While the mechanism with three degrees of freedom is constructed byadding a rotary or linear motion to the mechanism with two degrees offreedom in the embodiments described above, the invention is not limitedthereto. The linkage system can have a mechanism with four degrees offreedom by adding both rotary and linear motions to the mechanism withtwo degrees of freedom.

1. A linkage system comprising: an input member disposed on an inputside; an output member disposed on an output side; and three or morelink mechanisms, each link mechanism consisting of end links rotatablycoupled to the input member and the output member, respectively, acenter link rotatably coupled to the end links on the input side and theoutput side, and four revolute joints by which the end links arerotatably coupled to the input and output members, and to the centerlink, the link mechanism being geometrically identical with respect to acenter cross-sectional plane relative on the input and output sides,wherein each of the revolute joints of the link mechanism includesbearings that support at both ends of the revolute joint.
 2. A linkagesystem according to claim 1, wherein the revolute joints of the linkmechanism are detachable from the links.
 3. A linkage system accordingto claim 1, wherein rotation angle sensing means for measuring therotation angle of the end link are provided at the revolute jointsbetween the input member and two or more end links.
 4. A linkage systemaccording to claim 3, wherein the rotation angle sensing means comprisesa sensor and a sensed part respectively placed in a rotating part and astationary part opposite each other.
 5. A linkage system according toclaim 2, wherein rotation angle sensing means for measuring the rotationangle of the end link are provided at the revolute joints between theinput member and two or more end links.
 6. A linkage system according toclaim 5, wherein the rotation angle sensing means comprises a sensor anda sensed part respectively placed in a rotating part and a stationarypart opposite each other.
 7. A linkage system according to claim 1,wherein the orientation of the output member is determined from anequation representing the correlation between the orientation of theoutput member defined by a bending angle {umlaut over (γ)} and arevolution angle f and rotation angles ÿn of the end links on the inputside:cos(ÿ/2) sin ÿn−sin (ÿ/2) sin (f+ÿn) cos ÿn+sin (g/2)=0 where g is anaxial angle between the two coupling shafts at both ends of the centerlinks, and ÿ is a distance angle of circumferential distance of each endlink from a reference end link.
 8. A linkage system according to claim1, wherein actuators are connected to the end links on the input sidethrough rotary transmission components.
 9. A linkage system according toclaim 1, wherein actuators are connected to the end links on the inputside through rotary transmission components.
 10. A linkage systemaccording to claim 1, wherein the orientation control of the outputmember is achieved by reverse conversion using an equation representingthe correlation between the orientation of the output member defined bythe bending angle ÿ and the revolution angle f and the rotation anglesbn of the end links on the input side:cos(ÿ/2) sin ÿn−sin (ÿ/2) sin (f+ÿn) cos ÿn+sin (g/2)=0 where g is theaxial angle between the two coupling shafts at both ends of the centerlinks, and ÿ is the distance angle of circumferential distance of eachend link from a reference end link.
 11. A linkage system according toclaim 1, wherein any one of the input member and the output membercomprises a rotating mechanism that makes the output member rotatearound its center axis.
 12. A linkage system according to claim 1,wherein any one of the input member and the output member comprises arotating mechanism that makes the output member rotate around its centeraxis.
 13. A linkage system according to claim 1, wherein any one of theinput member and the output member comprises a rotating mechanism thatmakes the output member rotate around its center axis.
 14. A linkagesystem according to claim 1, wherein the rotating mechanism that makesthe output member rotate around its center axis includes rotation anglesensing means for measuring the rotation angle thereof.
 15. A linkagesystem according to claim 1, wherein the orientation of the outputmember is determined from an equation representing the correlationbetween the orientation of the output member defined by the bendingangle q_(L), the revolution angle f_(L), and a surface rotation angleh_(L) of the output member, and the rotation angles ÿn of the end linkson the input side:cos(ÿ _(L)/2) sin ÿn−sin(ÿ _(L)/2) sin(f _(L) +ÿn) cos ÿn+sin (g/2)=0where g is the axial angle between the two coupling shafts at both endsof the center links, and ÿ is the distance angle of the circumferentialdistance of each end link from a reference end link; andh_(L)=f_(L).
 16. A linkage system according to claim 1, wherein theorientation of the output member is achieved by reverse conversion usingan equation representing the correlation between the orientation of theoutput member defined by the bending angle ÿ_(L), the revolution anglef_(L), and a surface rotation angle h_(L) of the output member, and therotation angles ÿn of the end links on the input side:cos(ÿ _(L)/2) sin ÿn−sin(ÿ _(L)/2) sin (f _(L) +ÿn) cos ÿn+sin (g/2)=0where g is the axial angle between the two coupling shafts at both endsof the center links, and ÿ is the distance angle of the circumferentialdistance of each end link from a reference end link; andh_(L)=f_(L).
 17. A linkage system according to claim 1, wherein theorientation of the output member is achieved by reverse conversion usingan equation representing the correlation between the orientation of theoutput member defined by the bending angle ÿ_(L), the revolution anglef_(L), and a surface rotation angle h_(L) of the output member, and therotation angles ÿn of the end links on the input side:cos(ÿ _(L)/2) sin ÿn−sin(ÿ _(L)/2) sin (f _(L) +ÿn) cos ÿn+sin (g/2)=0where g is the axial angle between the two coupling shafts at both endsof the center links, and ÿ is the distance angle of the circumferentialdistance of each end link from a reference end link; andh_(L)=f_(L).
 18. A linkage system according to claim 1, wherein a lineardrive mechanism is provided to any one of the input member, the outputmember, and the center links.
 19. A linkage system according to claim 1,wherein a linear drive mechanism is provided to any one of the inputmember, the output member, and the center links.
 20. A linkage systemaccording to claim 1, wherein a linear drive mechanism is provided toany one of the input member, the output member, and the center links.21. A linkage system according to claim 1, wherein a linear drivemechanism is provided to any one of the input member, the output member,and the center links.
 22. A linkage system according to claim 1, whereina linear drive mechanism is provided to any one of the input member, theoutput member, and the center links.
 23. A linkage system according toclaim 1, wherein a linear drive mechanism is provided to any one of theinput member, the output member, and the center links.
 24. A linkagesystem according to claim 1, wherein any one of the input member and theoutput member include a torque sensor so as to detect torque input fromthe other one that is not provided with the sensor.
 25. A linkage systemaccording to claim 1, wherein any one of the input member and the outputmember comprises a rotating mechanism that makes the output memberrotate around its center axis.
 26. A linkage system according to claim1, wherein any one of the input member and the output member comprises arotating mechanism that makes the output member rotate around its centeraxis.
 27. A linkage system according to claim 1, wherein the rotatingmechanism that makes the output member rotate around its center axisincludes rotation angle sensing means for measuring the rotation anglethereof.
 28. A linkage system according to claim 1, wherein theorientation of the output member is determined from an equationrepresenting the correlation between the orientation of the outputmember defined by the bending angle q_(L), the revolution angle f_(L),and a surface rotation angle h_(L) of the output member, and therotation angles ÿn of the end links on the input side:cos(ÿ _(L)/2) sin ÿn−sin(ÿ _(L)/2) sin (f _(L) +ÿn) cos ÿn+sin (g/2)=0where g is the axial angle between the two coupling shafts at both endsof the center links, and ÿ is the distance angle of the circumferentialdistance of each end link from a reference end link; andh_(L)=f_(L).
 29. A linkage system according to claim 1, wherein theorientation of the output member is achieved by reverse conversion usingan equation representing the correlation between the orientation of theoutput member defined by the bending angle ÿ_(L), the revolution anglef_(L), and a surface rotation angle h_(L) of the output member, and therotation angles ÿn of the end links on the input side:cos(ÿ _(L)/2) sin ÿn−sin(ÿ _(L)/2) sin (f _(L) +ÿn) cos ÿn+sin (g/2)=0where g is the axial angle between the two coupling shafts at both endsof the center links, and ÿ is the distance angle of the circumferentialdistance of each end link from a reference end link; andh_(L)=f_(L).
 30. A linkage system according to claim 1, wherein theorientation of the output member is achieved by reverse conversion usingan equation representing the correlation between the orientation of theoutput member defined by the bending angle ÿ_(L), the revolution anglef_(L), and a surface rotation angle h_(L) of the output member, and therotation angles ÿn of the end links on the input side:cos(ÿ _(L)/2) sin ÿn−sin(ÿ _(L)/2) sin (f _(L) +ÿn) cos ÿn+sin (g/2)=0where g is the axial angle between the two coupling shafts at both endsof the center links, and ÿ is the distance angle of the circumferentialdistance of each end link from a reference end link; andh_(L)=f_(L).
 31. A linkage system according to claim 1, wherein a lineardrive mechanism is provided to any one of the input member, the outputmember, and the center links.
 32. A linkage system according to claim 1,wherein a linear drive mechanism is provided to any one of the inputmember, the output member, and the center links.
 33. A linkage systemaccording to claim 1, wherein a linear drive mechanism is provided toany one of the input member, the output member, and the center links.34. A linkage system according to claim 1, wherein a linear drivemechanism is provided to any one of the input member, the output member,and the center links.
 35. A linkage system according to claim 1, whereina linear drive mechanism is provided to any one of the input member, theoutput member, and the center links.
 36. A linkage system according toclaim 1, wherein a linear drive mechanism is provided to any one of theinput member, the output member, and the center links.
 37. A linkagesystem according to claim 1, wherein a linear drive mechanism isprovided to any one of the input member, the output member, and thecenter links.
 38. A linkage system according to claim 1, wherein alinear drive mechanism is provided to any one of the input member, theoutput member, and the center links.
 39. A linkage system according toclaim 1, wherein a linear drive mechanism is provided to any one of theinput member, the output member, and the center links.
 40. A linkagesystem according to claim 1, wherein a linear drive mechanism isprovided to any one of the input member, the output member, and thecenter links.
 41. A linkage system according to claim 1, wherein alinear drive mechanism is provided to any one of the input member, theoutput member, and the center links.
 42. A linkage system according toclaim 1, wherein a linear drive mechanism is provided to any one of theinput member, the output member, and the center links.